1. Field of the Invention
This invention relates to a rotating blade damper for an air handling system. More particularly, this invention relates to a rotating blade fire or smoke damper with an improved mechanism for locking the blade of a single blade damper, or a blade of a multiple blade damper with position interlocked blades, in its closed, flow blocking position after the movement of the blade to such position due to a fire or other condition of excessive temperature.
2. Description of the Prior Art
U.S. Pat. No. 3,650,069 (Alley) describes a fire damper with a rotating blade. The rotating blade of the damper of this reference is normally held in an open, flow permitting position by a mechanism which includes a fusible link. The fusible link will fail in the event of a fire or other condition of excessive temperature, whereupon the blade will rotate to its closed, flow blocking position to prevent the passage of smoke through the duct in which the damper is placed. In the fire damper of this reference the blade is latched in its closed position by a latch mechanism which is carried by the blade and which is, therefore, exposed to the full effects of the high temperature condition within the duct. This can lead to warpage or other thermal damage to the latch mechanism, and it partly obstructs fluid flow through the damper when the blade is in its open position.
U.S. Pat. No. 4,338,967 (McCabe) discloses a multiple blade, rotating blade air, smoke or fire damper in which a double link, knee action joint mechanism retains each blade in its closed, flow blocking position. Each knee action joint is in an over center condition when the blade operated thereby is in its closed position. Such over center condition provides some slop in the position of the blade when it is closed, which permits the blade to back off slightly from its fully closed position. This condition can lead to smoke leakage past the blade and vibration or chattering of the blade within the damper. Further, the damper of this reference is motorized, and modern industrial or safety requirements often preclude the use of motorized fire dampers.